The invention relates to an internal combustion engine with a crankcase and a cylinder head having exhaust ports which feed into an exhaust manifold for exhaust gas from combustion chambers of the internal combustion engine. The invention further relates to a method for operating an internal combustion engine.
Internal combustion engines of the afore-mentioned type are known in the art. They include, in particular, the crankcase, also referred to as engine block, and the cylinder head. The crankcase and the cylinder head jointly form the combustion chambers of the internal combustion engine, with the crankcase for example at least largely including the combustion chambers in the form of open-edged recesses in the direction of the cylinder head and with the cylinder head merely closing the latter. The crankcase may further include a cooling jacket and an engine casing of the internal combustion engine. Gas exchange members of the internal combustion engine are oftentimes provided in the cylinder head, i.e. in particular valves. The gas exchange members are provided for intake or discharge of air or exhaust gases into the combustion chambers. A camshaft of the internal combustion engine may also be arranged in the cylinder head. Exhaust gas flows out of the combustion chambers of the internal combustion engine, in particular via the gas exchange members, into the exhaust ports. From there, it enters the exhaust manifold and then in an exhaust gas tract of the internal combustion engine for subsequent release into the environment of the internal combustion engine, in particular via an exhaust gas purification device.
In a warm-up operation of the internal combustion engine, i.e. at low temperature of the internal combustion engine, undesirable friction forces are produced in the latter, for example between the walls of the combustion chambers and pistons arranged in the combustion chambers. It is therefore the objective to increase the temperature of the internal combustion engine as quickly as possible and thus to shorten the warm-up operation so as to minimize the frictional forces. Exhaust gas flowing out the combustion chambers of the internal combustion engine rapidly heats up as a consequence of combustion processes taking place in the combustion chambers. It is therefore known in the art, for example from DE 33 22 063 A1, to use the temperature of the exhaust gas to heat the lubricating oil of a lubricating oil circuit of an internal combustion engine. For this purpose, the mentioned document describes the provision of a heat pipe between exhaust-gas-carrying parts and the lubricating oil circuit. However, this approach has the disadvantage that the transmitted heat flow (heat quantity per unit time) is limited by the heat pipe on one hand, and the lubricating oil is merely heated on the other hand so that the warm-up operation of the internal combustion engine is only slightly shortened and frictional forces are only indirectly influenced.